What now!
Thread Starter
|
Tuned
Joined: Aug 2007
Posts: 287
Likes: 1
What now!
*1988 f250 351W
I changed out my plenum gasket which was leaking like around the rear 4 ports. I used high-tack and I thought I had the low vacuum issue handled. Next day the truck ran good pulling 17" to 18" vacuum. Codes showed no #41 lean condition so I thought I had it nailed. No nasty too rich smell out the exhaust either for the first time in years. Next day it started again. The #41 code came back during the KEOER test. Vacuum still was around 17 to 18" but too much fuel casuing surging idle. Fuel rail showed 34 PSI steady.
I pulled all the vacuum lines and pluged the plenum ports with no change. The only part left is the IAC which I changed once before I found the plenum gasket leak but I returned since I couldn't see any change.
So before I change the IAC for a second time I decided to try spraying carb cleaner around just for the fun of it. When I removed the intake air filter hoses from the throttle body with the truck running and spayed short bursts of carb cleaner at the closed throttle plates the idle smoothed out and the vacuum went steady at 20". If I over sprayed the carb cleaner the truck would almost stall as expected.
What's going on here? Are the trottle plates leaking too much air or is the old IAC at fault.
Thanks for all the ideas to date. I'm closer to sloving the problem than I was!
Jim
I changed out my plenum gasket which was leaking like around the rear 4 ports. I used high-tack and I thought I had the low vacuum issue handled. Next day the truck ran good pulling 17" to 18" vacuum. Codes showed no #41 lean condition so I thought I had it nailed. No nasty too rich smell out the exhaust either for the first time in years. Next day it started again. The #41 code came back during the KEOER test. Vacuum still was around 17 to 18" but too much fuel casuing surging idle. Fuel rail showed 34 PSI steady.
I pulled all the vacuum lines and pluged the plenum ports with no change. The only part left is the IAC which I changed once before I found the plenum gasket leak but I returned since I couldn't see any change.
So before I change the IAC for a second time I decided to try spraying carb cleaner around just for the fun of it. When I removed the intake air filter hoses from the throttle body with the truck running and spayed short bursts of carb cleaner at the closed throttle plates the idle smoothed out and the vacuum went steady at 20". If I over sprayed the carb cleaner the truck would almost stall as expected.
What's going on here? Are the trottle plates leaking too much air or is the old IAC at fault.
Thanks for all the ideas to date. I'm closer to sloving the problem than I was!
Jim
